A reliable and valid protocol for measuring maximal oxygen uptake in pigs

Most knowledge about cellular and molecular adaptation in the heart after exercise training comes from rodent models, and this has substantially improved our knowledge about exercise-induced cardiac adaptations. However, in rodents, the electrophysiological properties of the heart are different from the human heart. Therefore, the need of exercise-training models in larger animal models is obvious. Physiological studies of cardio-respiratory fitness require training regimens that give robust and adequate testing procedures to quantify the outcome.

We developed a valid and reproducible protocol for measuring maximal oxygen uptake (VO_2max) in young pigs. As previous studies have exercised pigs using horizontal treadmills, we determined whether treadmill inclination may influence the level of peak oxygen uptake (VO_2peak) achieved, and whether the true VO_2max was reached. Eight young pigs were used. Submaximal and VO_2peak were tested at five different inclinations from 13 to 30°.

At submaximal VO₂, there was an excellent test-retest at all treadmill inclinations (r  ² = 0.99, coefficient of variation = 1.8%). The level of VO_2peak was dependent upon treadmill inclination and the true VO_2max, defined as a levelling-off of VO₂ despite increased running speed, was only reached a treadmill inclination of 24°. For VO_2peak we only observed a significant test-retest correlation when using 19 and 24° inclination of the treadmill (r  ² = 0.88, coefficient of variation = 9.7%).

The use of inappropriate treadmill inclination might hide training-induced adaptations if the true VO_2max is not reached. This study shows that the present test protocol can be used in future studies of exercise on treadmill, when the aim is to measure submaximal and VO_2max in pigs.